Periodically sell Littler as the crème de la crème (5)
I believe the answer is:
elite
'the creme de la creme' is the definition.
(I've seen this before)
'periodically sell littler' is the wordplay.
'periodically' indicates alternate letters (letters must be selected 'every so often').
'sell'+'littler'='selllittler'
The alternate letters of 'selllittler' are 'ELITE'.
'as' is the link.
(Other definitions for elite that I've seen before include "Superior or favoured group of people" , "12 letters = 1 inch (type)" , "Letter size; superior group" , "Exclusive set" , "Aristocratic" .)